Long-term time series of environmental tracers reveal recharge and discharge conditions in shallow karst aquifers in Hungary and Slovakia

Hydrochemical and Isotopic Difference of Spring Water Depending on Flow Type in a Stratigraphically Complex Karst Area of South Korea

“…The fast infiltration from surface was supported by the tritium concentrations (Figure 5A) similar to the 3 H levels around 10 TU in precipitation during the study period in South Korea (Chae and Kim, 2019). Type Ⅰ also showed relatively high tritium concentrations but less than Type Ⅱ, which suggests the recent or short-circulating discharge of meteoric water occurring at both springs (Palcsu et al, 2021). In summary, the Type Ⅱ springs seemed to be fed by both deep groundwater and recent conduit flow (Figure 8) as in Lorette et al (2018) who suggested that Toulon Springs are fed by two aquifers: (i) the Jurassic confined karst aquifer responsible for low-water period and related to dolomitic hydrochemical characteristics, and (ii) the upper Cretaceous unconfined aquifer responsible for quick hydrodynamic and hydrochemical variations.…”

“…− can be indicators of agricultural contaminants (Schilling and Helmers, 2008;Kim et al, 2021). Consistently, the deep groundwater had lower tritium contents (3.3-6.7 TU) than the shallow groundwater (8.7-9.4 TU) (Figure 5A), indicating relatively old ages (Palcsu et al, 2021), and high δ 13 C DIC up to −10.0‰ (Figure 5B), implying a larger carbonate dissolution effect. According to Marfia et al (2004), the DIC in groundwater evolves initially under open system conditions (δ 13 C DIC of −25 to −17‰), and later under closed system conditions as the δ 13 C DIC increases (δ 13 C DIC of -17 to -13‰) as a result of carbonate dissolution.…”

“…Doctor et al (2006) used the δD and δ 18 O of water and δ 13 C of dissolved inorganic carbon (DIC) as well as major ion chemistry to estimate mixing proportions among multiple sources, and found that water released from storage within the epikarst may comprise as much as two-thirds of conduit flow in a karst aquifer following rainfall. Palcsu et al (2021) found the 10% of the discharge water with a residence time of half a year and the contribution of an older component based on the seasonality of δ 18 O in 2015-2018 at a karst spring with an average discharge of 20 L/min in Hungary. Lorette et al (2018) found high Mg 2+ and low dissolved oxygen (DO) during low-water periods and explained the uncommon hydrochemistry using the mixture with a Jurassic confined aquifer in western France.…”

“…Subsurface flow in karst aquifers is mainly characterized by monitoring the hydrological (e.g., discharge), hydrochemical (e.g., cations and anions), and isotopic (mainly, δD, δ 18 O, and δ 13 C) variability of spring water that is groundwater naturally emerging to the surface (e.g., Lee and Krothe, 2001;Aquilina et al, 2005;Barbieri et al, 2005;Aquilina et al, 2006;Doctor et al, 2006;Moore et al, 2009;Jiang et al, 2013;Lorette et al, 2018;Gil-Márquez et al, 2019;Rusjan et al, 2019;Palcsu et al, 2021). For instance, Moore et al (2009) identified water sources (e.g., deepwater upwelling) and their mixing and interactions with aquifer materials based on hydrochemical data to understand the relationship between spring characteristics and the complexities of karst aquifers.…”

Karst Recharge Areas Identified by Combined Application of Isotopes and Hydrogeological Budget

“…Several of the isotope-based techniques involve interpreting differences between the isotopic compositions of rainfall and groundwater samples [10,40,41]. However, in this paper, the preliminary check procedure analyses how the single affecting factor (seasonal and amount effect) that leads the variability of the rainfall's isotopic composition can influence the isotopic composition of the spring waters.…”